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Renato Crispo, 19th century
Wood and rope, radius 22 cm
Room 9, showcase 2 (inv. no. 4124)
Donation Renato Crispo, 1993
At the time of sailing ships, this device was used to estimate the route sailed.
A wooden tablet on which the compass rose was either painted or engraved, the rhombuses (the 32 reference directions) each bore a series of eight holes. During the 4-hour watch, at the end of every half hour (measured with an hourglass), the helmsman inserted a peg in one of the holes in the rhombus corresponding to the direction of the ship's wake (read on the compass); a second peg noted the average speed, measured with the ship’s “log”.
The recording device was used for the "handover" between sailors who were often illiterate. The pilots would later reconstruct the daily route and record the data on the navigation plan, in order to record and correct the inevitable deviations from the planned route.